1. Field of the Invention
This invention relates to an antenna unit, more particularly to an antenna unit with a parasitic coupler.
2. Description of the Related Art
FIG. 1 illustrates a conventional dual-band antenna unit mounted in a notebook computer 1. The notebook computer 1 includes a lower housing 12, a keyboard 16 mounted on the lower housing 12, an upper housing 11 coupled pivotably to the lower housing 12, a liquid crystal display (LCD) 17 mounted on the upper housing 11, a grounding plate 18 mounted in the upper housing 11, an image-capturing device 19 mounted on the upper housing 11 and disposed above the grounding plate 18 between upper left and right corners of the upper housing 11, and a securing member 15 that secures the grounding plate 18 and the image-capturing device 19 on the upper housing 11. The conventional antenna unit includes left and right antennas 14, 13, each of which is a planar inverted-F antenna (PIFA) and is connected to the grounding plate 18 via the securing member 15. The left antenna 14 is operable within the 2.4 GHz bandwidth and is disposed adjacent to the upper left corner of the upper housing 11, whereas the right antenna 13 is operable within the 5.0 GHz bandwidth and is disposed adjacent to the upper right corner of the upper housing 11.
The aforementioned conventional antenna unit is disadvantageous in that the left and right antennas 14, 13 have a relatively large physical size. Moreover, the securing member 15 undesirably affects transmission and reception of signals by the left and right antennas 14, 13, and thereby decreasing efficiencies of the left and right antennas 14, 13.
To solve the above problem, as illustrated in FIG. 2, it has been proposed to place both the left and right antennas 14, 13 in close proximity, remove the securing member 15, and connect the left and right antennas 14, 13 directly to the grounding plate 18. This configuration, however, can cause other problems. Particularly, interference is generated between the signals associated with the left and right antennas 14, 13. Moreover, since this conventional antenna unit is not secured on the upper housing 11, the left and right antennas 14, 13 are easily deformed during assembly.